Worlds Collide
by You're-Casually-Cruel
Summary: It's been a year after the wars ended or so they thought. This time demigods and shadowhunters' world collide and have to ally themselves to defeat the new enemy.
1. Chapter I - The Fateful Night

**Worlds Collide**

**Disclaimer: I do not own the characters of Heroes of Olympus and Mortal Instruments. The two series belong to their rightful owners. I might alter something from the original story, if that bothers you I'm sorry but it's my story and I get to write whatever I want. This story is written purely for fun as a fan of the two series. Have fun reading! ^_^**

**Summary: It's been a year after the wars ended or so they thought. This time demigods and shadowhunters' world collide and have to ally themselves to defeat the new enemy.**

_**Chapter One**_

_**The Fateful Night**_

C

A

S

S

Y

My name is Cassandra McQueen, everybody call me Cassy though. I'm a daughter of Poseidon and yes, Percy Jackson was my half-brother. We never know each others' existence until last summer before I turned fourteen, a guy –I later found out was a satyr– came to our house to pick me up to bring me to a summer camp, which was not new to me since my mom always enrol me to a summer camp ever summer. Like most demigods, my mom never told me who my father was, only that she had a short-live affair with him. She said that they met after he watched her performance on a musical play in West End. My mom was British but after I was born we moved to New York, where she continued her career as a Broadway singer.

I can't believe how my life suddenly took a one hundred eighty degree in a matter of months after finding out what I really am. It was a lot to take in at first; to find out I'm a demigod, my father was Poseidon the god of the sea and I had a half-brother. But with Percy and his girlfriend, Annabeth's help, I was able to quickly adapt being a demigod. And Percy? He was the older brother I've always wanted to have, but I'll never ever say that to his face. He was very easy to get along with and very funny too.

I remember the night I was claimed by our father, he was grinning at me like he was really happy to have me as his half-sister. Later that night we walked down the beach to have a brother-and-sister-get-to-know-each-other bonding time. For the first time since I arrived in Camp Half-Blood, I saw him looked serious.

"You didn't look surprise when I was claimed by Poseidon." Not that I don't want to call him dad, it just felt weird to call someone you never know and never believe exist to call as my father.

"It's your eyes." Percy said like it was very obvious. "A year ago dad told me that he'll send me brothers and sisters next summer. I thought he was only kidding." He told me.

"Because you don't like to have another brothers and sisters?" I asked.

He looked down at me and it suddenly struck me how our sea green eyes were so alike, a thing we both inherit from our father but aside from that we don't have anything else in common when it comes to physical appearance. While he had a hair as black as a raven's feather, my hair was as white as snow, forming a halo like illusion around my head.

"No, I actually enjoy having a sibling. You had another brother Tyson, he's a Cyclops and often come here to visit me but right now he works for dad." He said with a small smile as if remembering our brother.

"A Cyclops?" I repeated, my facial expression must be a mixed of disbelief and horror because he laughed at me. "They are monsters, right?" I thought he was making fun of me.

"Yup, for both of your questions." He answered. "You've got nothing to worry about though, Tyson's great brother. I'm sure he'll be very happy to meet you." He assured me. I just nodded then we walked in comfortable silence as we go back to our cabin.

Percy was walking me to the subway after I ate dinner with his mom, stepfather and him at their house (They live in Manhattan while my mom and I live in Queens), when were about to walk pass an alley we heard a commotion followed by a blonde teenage boy that wore all black flipping through the air, and landing right in front of us, his back facing us. The guy must be a demigod or a gymnast to be able to do such stunt, not to mention gracefully.

Percy hastily moved in front of me, keeping himself between me and the blonde boy. I saw him draw out riptide out of his pocket ready to uncap it any second now. In reflex, my hand immediately flew and gasped the trident pendant of my necklace, my weapon that turned onto any weapon I want it to be; it was a gift came from my father. The boy seemed to not notice us or he didn't care about us standing there beside him. He pulled out a dull tube like dagger from his belt that holds more weapons.

"Asariel." The boy called out at that instant the blade of the dagger he was holding glowed brightly, blinding Percy and I for a moment. Then the boy dashed back into the alley, where we saw him came out.

This time Percy uncapped riptide, turning the ballpoint pen to a Celestial Bronze sword. I also tugged my necklace and commanded it to turn to a sword. He glanced back to me and asked, "Ready for some action, little sis?"

I nodded then we both run after blonde boy. It was one of the things I really love about my brother, even though he was protective of me he will never tell me to stay on the sidelines because he trust me that I can take care of myself and it was in our nature, to fight.

In the alley, there was a small group of monsters with claws and there were jets of flames from their empty eye sockets. I never saw monsters like this before, even illustrations in books back in camp. Blonde boy was slicing and stabbing the monsters efficiently like he'd been doing it his whole life and maybe he does.

Percy seemed to not care about not recognizing those monsters; his natural warrior instinct simply took over, probably telling him to just kill the monsters. I also didn't waste any more time figuring out what was their name and sprang into action. I have never been into a quest but I've fight my fair share of monsters and my brother personally trained me, so I can say that I'm a good fighter.

The monster tried to claw me but I chopped its hand and cut the head then it just vanish without turning into sand, which confused me more. I didn't have the time to think about what those creatures were, another monster that jump at me. I rolled to the side away from it then quickly went back to my feet and run straight to the monster. I stabbed it in the spine, just like the other one it just vanished leaving no trace of its existence.

I looked around me; there were only the three of us in the alley now. I noticed that my brother and blonde boy were sizing up each other now that there were no monsters left.

"Thanks for intruding my demon hunting." Blonde boy told us, his words dripping with sarcasm.

"You're welcome." Percy replied with the same tone casually shrugging his shoulder.

"Demon?" I repeated. Believing in myths is one thing but demons? My mind was racing with many questions.

"Don't tell me you didn't know what is the thing you just killed was?" He asked us in complete disbelief.

"They were monsters." Percy automatically answered.

Blonde boy laughed like it was the most hilarious thing he heard in awhile. "In a way they were, but the right term is demon." He corrected him. "You are not a mundane since you can obviously see me and can kill those demons. I don't think you're downworlders either. What are you? "

"What's a mundane? Downloaders, like a person who download something from the internet? And of course we can see you we are not blind."

Blonde boy smiled as if remembering a funny memory. I went to my brother's side and tugged at the sleeve of his shirt, he glanced at me and our eyes met, silently conversing how we should handle the situation.

"Mundane means normal and he said downworlders not downloaders." I whispered to him and he nodded.

Blonde boy was not a demigod that's for sure. I remember Percy telling me about the boy he met before that talked about Egyptians and the possibilities of another set of gods out there. What if this boy was also from different world from ours?

It seemed like it sunk in to Percy that this boy was not a demigod and thinking about the same thoughts as me. "Look, we didn't mean to get involve to your mons– demon hunting. We're just in the wrong place at the wrong time. It's for the best if we just forget this night happened." He said to blonde boy, uncapping riptide to turn it back to a pen and I did the same turning my weapon back as a necklace to show blonde boy were not a threat and telling the truth.

"Want to stay mysterious, so you get to see me again, huh?" Blonde boy smirked cockily. I find it hard to read whether he was joking or he was just really cocky.

"That is exactly what we're trying to avoid." Percy said, tucking his hands inside his jeans.

"And here I thought everybody find me charming."

"Sorry but I'm straight."

"I don't like boys." I replied, which was true but I won't deny that blonde boy was indeed charming, enchanting even.

"News flash I'm a boy." My brother pointed out.

"Well, I don't have much choice but to like you, do I?" I said. "Anyway, let's just go." I started to drag my brother out of the alley. I don't think blonde boy will attack us, for some reason I trust him not to harm us.

We reached the subway station; Percy hugged me tight then ruffled my braided icy white, hair to annoy me. "Quit doing that!" I complained.

"Have a safe trip." He told me after he let me go.

"You too, I don't think blonde boy will easily give up knowing who we are." I voiced out my worry.

"I know."

"Should we tell Chiron or Annabeth about what happened?"

He shook his head. "I don't want to worry them. Let's keep it to ourselves for awhile."

"Maybe we should investigate about it." I said, excitement was cursing through me with the thought.

"Not unless he becomes a threat, until then we'll leave him alone." He said authoritatively.

"Okay." I said a little disappointed. "I should get going, mom must be getting worried." I waved goodbye to my brother and went inside to go to the platform area.

**A/N: Hi! Thank you for reading my story! You have no idea how much that means to me! What do you think of my story? I know I'm not the best writer but I'm trying to improve. English is not my first language and I know it's not an excuse but please bear with me! ^_^**

**About Cassy: I always wanted Percy to had a half-sister because Jason had Thalia and Nico had Hazel, he is the only son of the big three that didn't have a sister in the series, so I think it will be cool if he also had one. **


	2. Chapter II - Jace vs Percy

**Worlds Collide**

**Disclaimer: I do not own the characters of Heroes of Olympus and Mortal Instruments. The two series belong to their rightful owners. I might alter something from the original story, if that bothers you I'm sorry but it's my story and I get to write whatever I want. This story is written purely for fun as a fan of the two series. Have fun reading! ^_^**

**_Chapter Two_**

**_Jace vs. Percy _**

J

A

C

E

I was watching the dark, hair boy watched Snow White left, heading to the subway station. They should have known better than think I'd easily give up knowing what and who they were. The boy started walking back to where he and Snow White came from when she was already out of our view. I silently followed him. He turned o an alley I know will lead him in a dead end. I can't help but smirked, the boy knew I'm following him and Snow White but instead of confronting me right away, he makes sure Snow White's safety first, something I approve, not that I had an intention of hurting them anyway. I just want some answers to my questions.

"I know you've been following us." He said, his back was turned to me but I saw his hand pulled out a pen, which was a sword he turned to a pen earlier. I've seen a lot of weapon in my life time – Maellartach (The Mortal sword) and Glorious – but never a sword that can turn into a ballpoint pen. What kind of magic do this boy and Snow White possess?

I moved out of the shadows, finding no reason to hide anymore that he busted me. I casually leaned on the wall, putting my hands inside my pocket to make me look bored. I must be getting rusty or this boy might be a very well trained soldier too like me. Even Snow White, who looked like she just stepped out from one of Izzy's fashion magazine, was good at fighting. I noticed a trident and SPQR mark on his forearm, which only made me more curious about them.

"Didn't you understand a single word we said to you?"

"What's the fun in that?"

He uncapped his pen, turning it to a bronze sword again. "Fine, I'll give you a good time." He charged to me and I quickly draw out a seraph blade, wishing I brought a sword with me to have a fair fight with him.

"Hagith." I named my seraph blade then it blazed up brightly. I blocked his sword with my dagger, our swords clashed with each other, forming a cross. I jumped back, away from him. We circled each other, waiting for the right opportunity to attack. Roman boy jumped at me and brought his sword across my chest, but I was able to stop the blade again just in time. I lunged but he easily dodged my attack then used his shoulder to push my back. I staggered forward, momentarily losing my balance.

When I find my footing again, I turned to face him, grinning broadly. He was good; I have to give that to him. It had been a long time since I met someone who can give me a fight this good. "You do know how to have a good time."

"You just don't know when to give up, do you?" He scowled.

"Give up doesn't exist in my vocabulary."

Roman boy was about to say something back to me but a familiar female voice interrupted it. "Am I late to the party?"

She was the girl with him earlier. I shook my head, still grinning. The girl reminded me of Clary, stubborn and always does the opposite of what you told her to do.

"Oh gods! What are you doing here? You're supposed to go home!" He scolded Snow White.

"And let you have all the fun?"

"We're not playing a game!"

"Someone's here!" I called their attention. They both turned their heads towards me.

"What do you want from us?" Roman boy asked me, sounding tired.

"I want to know what you are."

"It's too dangerous. So take my advice, forget about meeting us." He insisted.

"I face danger every day." I pointed out. "You just saw me hunt demon, don't you?"

The two of them shared a look, a silent conversation then Roman boy glared at me. Snow White seemed to be interested to know more about what I am as much as I want to know about what they are.

"Here's a deal. You get to ask us a question every time you answer one of ours." Snow White offered their proposition to me, obviously taking the reins from Roman boy. Thank the Angels; this boy had a girl who has brains with him to come up with a proposition like this.

"Deal." I agreed.

"What are you?" She immediately fired the million dollar question.

"I'm a shadowhunter. We're sometimes called Nephilim." I answered.

"A what?" Roman boy asked, a dumb look was on his face.

Snow White ignored her companion's question. "Aren't Nephilim described like monsters in the Bible?" She asked me, confusion was all over her beautiful face. Yes, she was beautiful and just because I have a girlfriend doesn't mean I can't appreciate to look at other girls every now and then, but still Clary will forever be the most beautiful girl I've ever seen.

"You read the Bible?" Roman boy asked her.

"Yes. You don't?"

"No, I don't. My mom didn't raise me religious."

"It's my turn to ask." I reminded them.

"Go ahead." She told me.

"What are you?"

They looked at each other again, which I'm slowly becoming irritated with. "We're demigods."

"Like the kids of the Greek gods with mortals in the mythology?" I asked. Okay, so the twenty question game was getting in my nerves. I want answers quick. Does this mean Greek gods really exist? It suddenly drowns to me the tenet of the Shadowhunters' belief. All stories are true. There was no one religion, no one truth and no myth lacked meaning. Isn't my race also a story ripped from the pages of the Bible? I wanted to laugh but too stunned to do so. (If you're familiar with the 'All stories are true' quote it came from City of Fallen Angels. Just to avoid being accused of plagiarism from the readers of the book. ^_^)

"My question first." She said.

I frowned, remembering her question earlier. "Do I look like a monster to you? You probably should blame it to the people that translate the Bible for describing us as monsters."

She nodded her head, whether because she understands my answer or she was pretending to understand it. "As for your question, yes, we are the off-spring of the gods and mortal from the Greek mythology." She answered.

"This is enough. You know now what we are and we know now what you are. Your curiosity must be satisfied now." Demigod boy interjected.

"Actually, I still have more questions." I told him. "Ask me any question."

"Correct me if I'm wrong, Nephilim are half-angel and half-human. Does that mean one of your parents is an angel?"

"In the Bible Nephilim were the offspring of human and angels, but Shadowhunters were created when Jonathan Shadowhunter summon the Angel Raziel, who mixed his own blood with the blood of men in the mortal cup, and gave to them to drink. Those who drink the angel's blood became shadowhunters, as did their children and their children's children." I answered, giving them the summary version of the story. "Who are you?" I asked since I'm getting tired of naming them Snow White and Roman/demigod boy.

"Who are you?" Demigod boy shot back to me.

"You know the rule; you need to answer my question first before I answer yours." I told him.

"As far as I can remember the rule said, you can ask as a question if you answer ours. We never say that we need to answer your questions at all." She clears it up. "But I'll tell you who I am. I'm Cassandra, everybody call me Cassy though."

"Cassandra, isn't she the insane sister of Paris?" I asked, recalling the story of Iliad that I've read when I was around nine.

She narrowed her eyes. "She's not insane but cursed." She defended.

"Wait! Don't tell me you are the original Cassandra?"

"Fortunately I'm not. I'm only named after her." She answered. "That's two questions for me. Who are you?"

"You can be a good trader, you know." I grinned. "I'm Jace Lightwood."

"Under normal circumstances, I'd say it's nice to meet you Jace but –" Cassandra was interrupted by Demigod boy.

"It's not nice to meet you at all."

She ignored what he said and changed the topic. "You said that those creatures we just killed were demons. What do you specifically call them? I've never seen those things before." she asked me.

"Ah. We call them Moloch demon. They like to fight in groups." I replied.

"Are we done with the history lesson?" Demigod boy asked with pure annoyance. Cassandra shot him a dirty look, and Demigod boy huffed but didn't make any comment.

"You said that you're an offspring of Greek gods but why is that you have a SPQR mark on your forearm? It stands for Senatus Populusque Romanus, if translated in English it's "The Senate and People of Rome", it's Roman."

"That's none of your business." Demigod boy said with complete irritation. I get that a lot, so it doesn't really bother me.

"It's his to explain not mine." Cassy agreed to him with a shrugged. "I guess that's all I can tell you about us."

"He still didn't tell me his name." I insisted, wanting to prolong the conversation for some reason.

"Jackson. Percy Jackson." He grumbled and for some reason Cassy laughed, ending up earning a glare from Percy. "Now you know what we are stop following us and forget about meeting us."

"It's for the better to keep our worlds apart from each other." She once again agreed to Percy.

"Why keep the two worlds apart?"

"The two worlds are separated for a reason. I don't know why and it's better to keep it that way." Percy answered as if he experienced meeting another world of different myth and it didn't end up very well.

"But we meet. I believe that it's because the two worlds are supposed to finally get to know each other." I reasoned out.

"Coincidence." He said but it seemed to me that he didn't believe his own words.

"There is no such thing as coincidence. And I agree with Jace, if the two worlds are not supposed to know about each others' existence the gods or someone will prevent it from happening. So why let us meet now? Someone made us meet on purpose." Cassy voiced out her opinion. She looked very young and yet she talked so intelligently. Snow White was slowly earning my respect and something about her made me want to protect her, not in a way I want to protect Clary because I love her but something else, like I'm suppose to know her.

"But who might that be? Any enemy you know?" I asked them.

"Just let it go." Percy said, still persistent about keeping the two worlds apart.

* * *

**A/N: Hi! Thank you for reading my story! What do you think of my story? ^_^**


	3. Chapter III - Perfect Strangers

**Worlds Collide**

**Disclaimer: I do not own the characters of Heroes of Olympus and Mortal Instruments. The two series belong to their rightful owners. I might alter something from the original story, if that bothers you I'm sorry but it's my story and I get to write whatever I want. This story is written purely for fun as a fan of the two series. Have fun reading! ^_^**

**_Chapter Three_**

**_Perfect Strangers_**

Part One

C

A

S

S

Y

Percy accompanied me home all the way from Manhattan to my mom and I's apartment in Queens. While we ride the F train, we've endlessly argued about Jace and the threats that he might bring if we try to get ourselves involve with his world. He also told me over and over again to avoid Jace if I ever see him again.

He only stay long in our apartment to explained to my mom why I got home late, altering the story by not mentioning about Jace, instead he told her that were attacked by monsters and he was worried that I might be attacked on my way home that's why he decided to accompany me. My mom was very fond of Percy, she treat him like her own son like how his mom treat me, the two woman were even good friends. I'd say that Poseidon had a good taste with women for choosing my mom and Sally, Percy's mom.

After Percy left, my mom told me she prepared the bath for me though it might be already cold by now. I told her that's fine since I can't just control water, I can also control its temperature –one of the perks of being a daughter of the god of the seas. I was bothered by Percy not mentioning about Jace and the demons we've encountered. I know that he means well, but I've never keep a secret from my mom although I know she keep a lot from me.

When I finished take a bath I've changed to my pyjamas then came out of the bathroom. My mom was waiting for me, sitting on the foot of my bed.

"Let me blow dry your hair." My mom offered, noticing my wet tangled mess of silver blonde hair, I got it from my mom but hers were a darker shade of blonde almost like the color of gold.

"Okay," I said. "I'll just go get the blower." I went back to the bathroom, fetching the blower. Then I came back to my bedroom handing the blower to my mom. My mom and I were both silent as mom blow dry and comb my hair, were always been close since it was just the two of us together that silence doesn't bother us.

The thought of meeting Jace was waiting on me. I felt like need to tell her about him, so I broke the silence. "Mom," I started to say with a soft voice.

"Yes, sweetheart?"

"There is something Percy and I leave out in the story we tell you," I admitted, looking down on my folded hands on my lap as I tell her about meeting Jace, his fight with Percy and our little exchange of information about our worlds. My mom stiffed, dropping the hair brushed on the floor. I turned around to look at my mom. Her face paled, her eyes wide with fear and her hands, no –her whole body was shaking.

"What's wrong?" I asked, panicking at the way my mom reacted as I mentioned meeting a shadowhunter.

My mom was still shaking as she crouched down to my level so were eye-to-eye, but even though she was looking at me it seemed like she was not seeing me but a distant painful past.

All I know about my mom's past was both of her parents were dead –never told me the cause of it– and that she used to work as a servant in West End theatre until the manager heard her singing while cleaning up the dressing room, since then she undergo vocal training and later on became one of the main cast of a musical. Her career as a Broadway singer in West End had been running for two years when she met my father.

"Mom?" I called again louder this time.

She seemed to snap out of her trance, but she looked like she was about to cry. "Percy's right, you should not intervene with the shadow world. Forget about it." She told me, her voice was quivering with emotion. "Promise me!" Then she stood up and hugged me so tightly as if she was afraid to lose me as she keep on telling me she love me.

I was so taken aback by my mom's reaction that all I did was nod my head. I know that my mom was one of those few mortals who have the ability to see through the mist and now she also knows about shadowhunters, even call their world shadow world. Why does she look so afraid when I tell her about meeting a shadowhunter? Did they do something wrong to her?

"Mom, what's wrong?" I murmured against my mom's embrace.

"Just promise me, Cassy." She repeated.

"Okay, I promised."

She let out a sigh of relief. "It's already late, you should go to sleep. Goodnight, sweetheart." She said and kissed me on the forehead before leaving my bedroom. And me on my own thoughts.

I lay down on my bed and stared at the ceiling, tonight's events made my nerves high-strung that I can't fall asleep then found myself sitting down on the bench of my upright piano. Before I know it my long, thin fingers started to glide on the familiar keys of the piano.

The earliest childhood memory I remember was when my mom sat me down on her lap at the age of three to taught me how to play the piano. Up to now it was the most precious memory I have, just my mom and I playing the piano together without a care about the world because we have each other and that was enough.

At one am, I finally felt sleepy, so I stopped playing the piano and crawled to my bed. Sleep immediately took me over as I close my eyes.

_The shivers that ran through my body were very violent because of the cold temperature of my surrounding. Why is it so cold in my bedroom? I thought to myself as I slowly open my eyes. I could only see nothing but darkness and I realized that I was not in my bedroom and I was lying on a damp cold ground that was hard on my back. I was only dreaming –more on having a nightmare. I sat down and tried to see through the darkness with no avail. _

_I heard a scary disembodied laugh. It was hard to pinpoint where the laughter came from because it was as if coming from all direction. _

_"Who's there?" I asked, my voice echoed through the darkness._

_"My return is coming near, daughter of Poseidon. Gaea was just an instrument I use to divert your attention from my rebirth." The gravelly voice told me and let out a booming laugh again. _

_The temperature went back to normal but I can still feel my body shivering, not from the cold this time but because of the disembodied voice that spoke to me. _

I suddenly sat upright on my bed breathing heavily covered with cold sweat and my throat was dry. I stood up from the bed and went to the bathroom to splash cold water on my face. I stared at my scared reflection on the mirror, remembering the stories Percy and Annabeth told me about when demigods have a dream it always mean something. But why in all of demigods there were, it had to be me to have such a disturbing dream? I wasn't able to go back to sleep after that.

_One week later…_

It was finally weekend; I usually spend it hanging out with Percy when I don't have much homework to do and today was one of those. Today I'm not just going to hang out like usually with Percy but will also talk to him about the nightmares I've been having every night this week.

I stepped out of the F train I always used as my form of transportation from Queens to Manhattan, when I noticed a figure with a golden blonde hair –Jace, he was leaning on the wall and his golden eyes met my sea green eyes, as he openly stare at me as I'm a puzzle he find so hard to solve.

Well, that made the two of us. But I made a promise to my mom and even Percy warned me to avoid him. Instead of approaching him, I willed myself to ignore him and continued to walk out of the subway station as if I didn't saw him standing there at all.

Of course, Jace didn't give up. He fell into step beside me, so much for my effort to ignore him. I noticed that for someone as good looking as Jace no one seemed to spear him a glace, although were in New York his looks will definitely catch someone's attention, right? My curiosity was starting to get the best of off me. I didn't speak to him until were in a corner where no one can see me talking to myself.

"Am I that remarkable good looking that you can easily pick me out from the crowd?" He said, smirking smugly down at me when I turned to face him.

I ignored what he said. "The mortals can't see you." I said matter-of-factly.

He shrugged. "I cast a glamour."

"What's a glamour?" I asked, not understanding what he was talking about.

"It's what made me invisible to the mundane." He answered.

"Ah. In our terminology it's called mist."

"I thought you'll ignore me."

"I plan to." I admitted, fidgeting with the strap of my messenger bag.

"Can't resist my charms?" He teased; his smirk was back on his face.

"Just curious."

"Curiosity kills the cat."

"If it wasn't for Isaac Newton's curiosity of the falling apple there will be no law of gravity." I countered.

Jace raised his eyebrows. "Have you ever used the law of gravity in your daily life?" He asked, looking very amused. "And didn't Isaac Newton die because of mercury poisoning out of his curiosity?"

I narrowed my eyes at him then can't help myself and end up laughing.

"I like you." He said with a sincere smile.

It was my turn to raise my eyebrow at him.

"Not that way." He cleared up. "I have a girlfriend."

"I know."

"How did you know?" he frowned.

"Good looking guys are either; taken, playboy or gay."

He burst out laughing. "True." He agreed. "So, you do think I'm good looking." He stated with a smug look

"Are you always this narcissistic?"

"Usually more." He answered. "Come, I've got something to show you." his tone change from being cocky to serious.

"I can't. I promise to avoid you." I protested, fidgeting with the strap of my bag again as avoid his eyes.

"And yet you're here talking to me."

"I really need to go, Percy's waiting for me." I started to walk away from him.

"You know I'll wait for you here every day if I have to." He called out to me, standing there look very arrogant because he knows that I believe he'll definitely do that

I sighed at his persistence. "Fine, I'll come with you just make it very quick, okay?" I said, giving up on his request to go with him. I noticed a passerby glance at me as if I lost my mind. "Come on, people are looking at me as if I'm going crazy talking to thin air." I motioned for Jace to walk ahead of me but kept his strides next to me.

Part Two

J

A

C

E

I thought Cassy will not come with me. She seemed to be very hesitant to talk to me unlike when we first met; she even took my side instead of Percy. I noticed the dark circles under her eyes due to lack of sleep, making me wonder what kept her awake all night but that was none of my business.

"Where are we going?" She asked me.

I was impressed how she was able to hold back this long before finally asking me where were going. "To the institute."

"What's the institute?" She was frowning was me as she asked.

"It's where shadowhunters live."

"Why are you taking me there? Aren't you afraid that we might attack you?"

"No, only with a shadowhunter blood can open the door of institute."

"How convenient," She murmured loud enough for me to hear. "But what if we bombard the institute with grenades and explosives?"

I chuckled at her ridiculous question. "You have a very wild imagination did you know that?"

"A lot of people said so." Cassy agreed dryly. "But seriously, why are you taking me there?"

"Because for some weird reason I trust you and I want you to trust me too."

After that we stayed silent the entire walk to the institute. We stopped in front of the gates of what looked like a rundown church to the eyes of the mundanes. She squint her eyes, trying to see through the glamour that surrounded the place. When the institute was stripped of its glamour the true vision of the place will appeared as an old gothic cathedral with soaring spires and a brass plate fixed on the wall next to the door was the institute's name.

"Annabeth will definitely love to see the design of this church." I didn't think that she mean to say it out loud while I fitted the key on the lock to open the heavy double doors.

We went inside and walked down the hallway. I watched Cassy study each glyphic of shadowhunter runes carved on every step of the winding stones stair as we climb up towards the elevator.

"Some of those symbols were tattooed to your skin." She observed. "What do they mean?"

"They are called runes and I'm not tattooed, I was marked." I corrected her.

"It's so confusing. Sometimes it's like you are talking in completely different language." She admitted.

"Be patient and I'll give you a shadowhunter 101 when we reach the library."

Come to think of it, it was easier to understand about demigods since there were books written about them available to read in every library and bookstore unlike about us shadowhunters, only we have the books about our race.

We reached the elevator and rode up in silence. The elevator stopped with a hissing stop and we were now on the entryway. Before I left to go to the subway everybody went out to do their own business. I hope that no one has returned yet.

We walked pass through one of the corridors that were lined with bedrooms then the mosaic of Angel Raziel holding the mortal cup and sward while emerging from the Lake Lyn and still she didn't asked a single question or utter a word. I found it weird how she listen to me and didn't continue to ask me questions.

We reached the arch-shaped wooden doors. I opened the door and we entered the circular library that was built inside a tower. The walls and shelves were lined with books from floor-to-ceiling that tall ladders were set. All of the books were hard bound with wither leather or velvet and didn't look only old but also well-used and had been well loved.

Cassy's eyes had a glimmer in them only those who adore books can possessed as she her gazed swept around the room, taking it all in with a complete awe on her face.

"You like to read books." I stated.

"I love to read books." She corrected. "My mom has those old classic novels and poetry books that she read to me at night. Those were also the same books I've first ever read." She confessed shyly.

I can't help but thought that her mother must be amazing to educate her child very well when it comes to literature. Cassy even read the bible considering that she was a demigod. It occurred to me that I didn't know who her godly parent was. "Who's your godly parent?" I asked her as we turned to the aisle where the codex was shelved.

"My father is Poseidon." She answered as if were just having a conversation about the weather while were drinking tea. I was speechless and that rarely ever happen.

I didn't exactly know who I expect to be her godly parent –I mean there was like hundreds of Greek god. But one thing was for sure, it never occurred to me that her father might be one of the most powerful Greek gods.

"Why are you staring at me like that?"

I shook my head and arranged my expression carefully. "Have you already met him?" I asked as I climbed up on the ladder to reach for the codex.

"Yes." She answered quietly without emotion just plain fact.

As I descend down the ladder, I heard Cassy let out a gasped that sounded like. "Blue!"

I looked at what caught her attention and saw Church curled up, lying on the floor. The cat must have felt our stare, it arched its neck, looking at us and yawned.

Cassy moved towards Church, crouching down to pet the stomach of the cat. It slit its eyes in pleasure, rolling over to get more comfortable position.

"Usually Church doesn't like people." I told her, leaning on the bookshelf.

She frowned. "You name your cat Church?"

"Church is already the cats name when I arrived here at the institute." I answered. "You also love casts?"

"I never had a pet growing up." She shared. "I have Porkpie now but he's Pegasus."

"You have Pegasus as a pet?" And here I thought nothing will ever surprise me anymore.

"Percy had a hellhound as a pet and the original Pegasus was my half-brother." I didn't said anything, just stood there looking at her.

She glanced at the book I was holding. "Shadowhunter Codex" she read the title of the book out loud.

I handed the book to her. "Everything you want to know about shadowhunters are there." I informed her.

"It's like the Pirata Codex in Pirates of the Caribbean." She commented.

"What's Pirates of the Caribbean?" I asked, not understanding what that was. "And I've never heard of the Pirata Codex."

"You didn't know the Pirates of the Caribbean movie? Or Johnny Depp?" She was looking at me like I came from another planet. It was the same look Simon would sometimes gave to me. "Pirata Codex in real life is called Boxer Codex."

"I think we have a copy of Boxer Codex somewhere."

Church seemed to be irritated that Cassy stopped paying attention to him/her anymore as we talked and decided to leave us alone, but Cassy didn't want the cat to go.

Cassy thrust the book back to me and chased after the cat. "Meow. Meow." She called Church but the cat ignored her.

"Cassy." I called, following them.

I stopped dead on my tracks as I saw Isabelle and Clary standing in the doorway staring at Cassy with bewildered expression.

"Who is she, Jace?" Isabelle asked, glaring at Cassy.

"Didn't you hear? She's Cassy." Clary responded. Her expression was carefully blank. Oh,shit! I immediately know I'm in trouble. This past week I've been out a lot, either search for Cassy or Percy and waiting for her on the subway station. I didn't tell anyone about meeting the two of them. Clary must be remembering the time I was avoiding her before. Her eyes and mine met briefly before she walked away from the us, down the corridor.

"What's going on Jace?" Isabelle demanded.

"Look, Izzy–" I ran my fingers through my hair in frustration as Cassy interrupted me.

"Chase after her. I'll explain to her what's going on." Cassy told me. I almost forgot that she was there. All I can think of was Clary walking away and hurting for nothing.

I gave Cassy a small but grateful smile before I took off, running after Clary. I reached Clary in time before the elevator doors open.

"Clary!" I grabbed her arm, stopping her from stepping inside the elevator.

"Is she the reason why you are gone a lot?" she asked me in an accusing tone.

"Yes, but not the way you think." I told her the story about how I met Cassy and explained the reason why I brought her here in the institute.

The relief was apparent on her face. "Why didn't you tell any of us about this?"

"I don't know." I answered honestly.

I cupped her face with my both hands and kissed her gently.

When we broke apart, Clary said. "Come on, let's go back there. I'm afraid what Isabelle might do to her."

"Right." Clary and I walked hand-in-hand back to the library to find Isabelle and Cassy getting along just fine. Isabelle was explaining to her the basic things that Cassy need to learn.

"What took the two of you so long?" Isabelle asked.

I ignored her inquisition. "What happen and it seem like you two are now good friends?"

"Well, she explained to me everything so we're cool now." Isabelle shrugged.

"Cassy, this is my girlfriend Clary. Clary, this is Cassy." I introduced the two girls to each other.

"I'm sorry about the drama earlier." Clary apologized to Cassy.

"It's alright." Cassy assured her.

Aloud ring of cell phone goes off. Cassy immediately dove through her messenger bag to search for her phone. We were alarm by her sudden panic when her phone started ringing.

"What's wrong?" I asked.

"Nobody calls my phone unless it's emergency." She explained.

She checked the screen of her phone and her expression turned to complete anxiety. She answered the call. I heard her say Percy's name with so much worry.

"Where are you?" She asked as she started to pace back and forth, running her fingers through her snow white hair.

Percy's answer only added worry to Cassy. "I'm not going without you!" She objected. "NO! Percy! Percy!" she looked at her phone as if she wanted to throw it away in frustration when Percy hung up the phone.

"Is Percy being attack?" I asked.

"Yes, I have to go. My brother needs me." She answered absentmindedly, putting her phone back to her bag and strapping it on her shoulder.

"Percy's your bother?" I asked, very surprise about it. They didn't look alike at all. I thought that they were friends or even a couple.

"Yes! I don't have time to answer all your questions."

"I'll come with you to help." I stated. "I bring you here after all."

"I don't want to involve you to our troubles."

"We like trouble." Isabelle said with a friendly smile.

"We can help to take you to your brother faster." Clary spoke up. "Tell me where he is and I'll open a portal for us to help him."

* * *

**A/N: Hi! Thank you for reading my story!**

**I realized that it was hard to write different POV's so I'll just stick to Cassy's.**

**Don't worry Cassy's not going to take Jace from Clary… ^_^**


	4. Chapter IV - Welcome To Camp Half-Blood

**Worlds Collide**

**Disclaimer: I do not own the characters of Heroes of Olympus and Mortal Instruments. The two series belong to their rightful owners. I might alter something from the original story, if that bothers you I'm sorry but it's my story and I get to write whatever I want. This story is written purely for fun as a fan of the two series. Have fun reading! ^_^**

**_Chapter Four_**

**_Welcome to Camp Half-Blood_**

C

A

S

S

Y

I felt like I plummet to a black hole after I step inside the portal. My stomach was still churning even after we arrived at Central Park, where Percy and I were supposed to meet.

Note to self: Travelling through a portal was not my thing. Same goes for riding boats for some ironic reason despite being a daughter of Poseidon.

A hand held my forearm to steady me on my feet. "Never use a portal before?" It was Jace, sounding a bit amused at my predicament.

I nodded my head, which only make me feel worst. "And not planning to step into one anytime soon again."

"My first time going through a portal didn't felt nice either." Clary told me sympathetically.

In the distance, loud cries of mortals were heard as they run away from the danger of a battle going on in the park. We all looked at each other before stared running towards the opposite direction where the mortals were heading. Even still far away I can now clearly distinguish where my brother was as he slashed through the giant man monsters with Riptide. . There were more than a dozen of them, attacking Percy and although he was a great fighter, it was obvious he was overwhelmed not just by the number of the enemy but also their size and strength. He looked tire, his clothes were torn, and he might be injured as well.

"Forsakens." I heard Isabelle called the giant man monsters.

I wanted to ask if they were demons called forsaken but didn't get the chance as the giant man monsters called, forsaken noticed us approaching them. At least were able to divert their focus on killing my brother.

I tugged my necklace and will it to take form as a bronze sword. I advance to the nearest forsaken and sliced it through its chest, it crumbled down to the ground. I saw the Isabelle wrapped her whip around the neck of a forsaken then with a flicker of her wrist the monster's head rolled off of its body.

Clary was doing well too, hitting her dagger in an arch to the forsaken's chest, but it only stagger backwards. The creature's knife blindingly sliced through the air but she quickly dodged the attack and pierced her dagger on the nape of the forsaken, killing it.

"Cassy!" Percy called out my name when he saw me as he jumped back away from the forsaken he was engaged with in a fight. He had a cut on his shoulder and too much blood was running down his arm.

"I'm sorry." I can't meet his eyes worried and guilt washed over me. Maybe if I listened to him and my mom about avoiding Jace he will not have to fight these forsakens. He will not be injured. We'll be both playing in the arcade or eating pizza while laughing at his stories and jokes. But thinking about those _maybes _will not do any of us good.

"There are too many of them." He pointed out, breathing heavily from the exhaustion of the fight and possibly because of his shoulder injury. "We can hail the Gray Sisters' taxi but we won't all fit."

"I can open a portal." Clary volunteered again.

"Can you open a portal in Long Island?" I asked her. I sounded like I was pleading but I don't care. "Percy's badly hurt, he need to be treated quickly." I added.

"You can't bring them to Camp." Percy objected, unstable on his feet now. I grabbed his arm, which was not connected to his injured shoulder to steady him. His face was pale and twisted in pain.

"They help us and your wound needs to be treated." I argued back.

"I don't trust them."

"It's not a matter of trust. They are our only way to get out of here alive."

"As you get older and experienced a lot of hardship in life, you'll soon find it hard to trust perfect strangers, Cassy."

I didn't respond to him. Percy rarely talked about his experience in a serious tone and I know that there were more storied about his adventures that he was not telling me.

"Clary, please open a portal to our Camp." I said quietly.

"I have to know where exactly to open a portal in Long Island. Describe to me the place as best as you could and I might know where it is." Clary said. I told her about the Delphi Strawberry Service, the cover up name of the Camp and thank the gods she knows the place. Clary started to work on drawing a rune to open a new portal that will lead us to Camp. Isabelle and Jace continued to fight the forsakens, I want to hep but I don't want to leave Percy's side either.

Clary finished opening the portal, motioning for Percy and I to go ahead first as she called for Isabelle and Jace to follow us immediately. Percy and I stumbled unceremoniously on the top of the Half-Blood Hill, the entrance of the camp, it was because my stomach turned again and my brother's deadweight on me.

Jace eased Percy off of me and wrapped my brother's uninjured arm around his to half-carry him. We walked down the hill pass the pine tree, entering the Camp.

"Is that what I think it is?" Isabelle asked, pointing to the Golden Fleece and its guardian dragon Peleus.

"Yes, it is." I answered.

We were halfway down the hill when I saw Connor Stoll and called him to for Chiron and medics. Moments later, two medics from the Apollo cabin took Percy away from Jace and a few other medics lead the four of us to the infirmary of the big house to treat our own injuries. There were a lot of campers milling around, intrigued by the situation.

I was sitting on the bed while a medic handed over the ambrosia and nectar to me for the injuries I got from fighting with the forsaken. I didn't even notice the cut on my forehead or the wound on my knees when Percy and I stumbled on the top of the hill after we went through the portal. All I could think of was my brother lying down on the bed next to me, being fed of ambrosia and nectar as well.

One of the medics was about to leave but I grabbed his arm. "How is he?" I asked.

"He's asleep now due to exhaustion." He answered and I let him go.

Jace and the two girls were also assisted by the medics but they told them that they can take care of their wounds. Clary pulled out a pen like thing and started to draw something on Jace's forearm.

"What's that?" I asked to divert my attention from Percy.

"It's a stele." Clary answered. "We use it to create runes and this rune is iratze, a healing rune." She explained to me as Jace took the stele from her to draw the same rune to her arm.

"Thanks for thinking about my welfare." Isabelle grumbled, tracing an iratze on her own arm to heal herself.

"You're already a big girl; you can take care of yourself." Jace shoot back not unkindly.

The door of the infirmary opened and Annabeth pushed through the medics, crowding around Percy's bed, Chiron wheeled inside behind her.

"Percy!" she shouted out my brother's name worriedly.

Chiron stopped in front of my bed. "Are you okay, child?" He asked me.

"Yes, I'm okay. Percy is the only one who seriously got hurt."

He looked at Jace, Clary and Isabelle, studying them thoughtfully with his ancient intelligent brown eyes. "It's been a long time since I last met a shadowhunter." He told them. "Welcome to Camp Half-Blood."

"Thank you." Jace replied politely.

"You do know about the existence of shadowhunters?" I stated a bit accusingly.

"Of course, being alive for thousands of years, you get to meet a lot of different human race and creatures you never thought exist." He answered. "But the two worlds are always been apart from each other because of their different beliefs."

"If so, why did Percy and I meet Jace?"

Chiron glanced at Percy's bed. It was only Annabeth sitting beside my brother's bed, holding his hand. He was sound asleep, probably from tiredness after battling almost a dozen forsaken alone. "We'll talk about it when Percy wakes up." He turned back to our direction and told us.

"Of course." I responded, hopping off of the bed to walk toward Percy's bed as Chiron carry on a conversation with the shadowhunters. I placed my hand on Annabeth's shoulder. "I'm sorry. I didn't listen to him and now his hurt." I told her quietly.

Annabeth reached for my hand to clasp it between hers. "It's not your fault. Trouble simply hugs your stupid brother like an old friend. I'm sure he'll survive." She said not without affection.

"That didn't sound so comforting." I muttered then introduced Annabeth to Jace, Clary and Isabelle. She thanked them for helping my brother and I to get here in the Camp.

"Cassy," Chiron called me. "Why don't you let them barrow some clothes to change in."

"Right." I agreed. "Annabeth, I'll come back later."

"Go ahead. I'll stay here." Annabeth assured me with a small smile.

Chiron moved to Percy's bed across from Annabeth and started talking to each other. I went back to Jace, Clary and Isabelle. "Come on." I cocked my head to the side where the door of the infirmary was.

The front of the big house was not crowded anymore like earlier. Most of the camp activities were back to normal, except for my best friend Leo, who was sitting on the deck waiting for us with a goofy grin on his face. Usually the sight makes me smile back but I'm too drained to put on a smile.

Leo was the first person I befriend in camp, I guess it was because were both lonely; me being the new kid on the block while he was left by his friends Piper and Jason, who moved to Camp Jupiter last summer. He was also the first person that didn't call me Percy's baby sister but called me Cassy instead.

"Hey, Cassy!" His grin faded when I didn't smile back at him. "Percy's fine, right?" He asked worried as well for my brother.

I shook my head and answered. "He's fine, asleep now though."

Leo's gazed move to my new friends next to me, or to be more precisely he was staring at Isabelle. His grin was back on his face as he strode towards her. I rolled my eyes, his obsession with girls that was either out of his league or had a boyfriend or both was acting up again.

"Hi! I'm Leo Valdez –" he started to introduce himself to her.

"Camp's repair boy." I snickered.

"Camp's repair boy." He repeated what I said without a thought then whipped his head to my direction when he realized what he just said, glaring at me. The nickname came from Piper and stick to Leo till now.

"What?"

I shrugged, beaming at him innocently.

"I'm son of Hephaestus." He continued, turning his gaze back to Isabelle, who look bored and wanted to get away from him. Yeah, definitely Leo's type of girl.

"He's my best friend." I told them. "Leo, this is my new friends Isabelle, Clary and Jace." I introduced them to each other.

"Are they also half-blood?" He asked.

"Nope." I answered. "It's a long story. Come along with us, I'll tell you the story on the way." I directed them to the shower area and along the way I've explained to Leo what Jace and the two girls were with their help. The campers stared at us as we walked but no one approached or talked to us. I asked Leo to bring Jace to the male shower area while the girls and I went to the female area. I told them to wait up for me as I quickly grabbed change of clothes to our cabin.

After we changed to fresh clean clothes, Jace into Percy's while Clary and Isabelle into mine. Clary and I were close to each other's size but to Isabelle my clothes were a size smaller than her actual size that her belly was showing on my camp shirt I let her borrow. And if Leo was not yet drooling at Isabelle earlier, he surely does now.

I don't whether should I sympathize my best friend because Isabelle didn't even spear him a glance or should I laugh at how pathetic he look like following around and trying to impress her.

"You do know that you're setting yourself up to disappointment, right?" I asked my best friend quietly as we walked back to the big house.

He sighed before answering my question. "I know." He admitted, looking down on his feet.

Isabelle spoke to him for the first time. "If I don't have a boyfriend right now I will surely take your advances and flirt back to let you believe that there is hope for us before I'll crush your heart with the heels of my stilettoes."

"That's blunt." I commented then looked at Leo to see if he was hurt by her statement, but he was in fact smiling at her.

"And that's Isabelle." Jace responded.

"Thanks." He said, ignoring what Jace said. "It's just that everyone seems to be in a relationship except for me."

"Being in a relationship isn't a trend, man. It's okay to be on your own." I told him.

Leo didn't answer and we continued to walk silently back to the big house.

"I'll go see my brother. Would you like to come or stay here?" I asked them.

"I'll go with you." Leo offered.

"We'll just stay here." Jace answered.

"Okay." Leo and I went inside the big house then went to the infirmary.

**A/N: Hi! Thanks for reading! ^_^**


	5. Chapter V - Curtains Up

**Worlds Collide**

**Disclaimer: I do not own the characters of Heroes of Olympus and Mortal Instruments. The two series belong to their rightful owners. I might alter something from the original story, if that bothers you I'm sorry but it's my story and I get to write whatever I want. This story is written purely for fun as a fan of the two series. Have fun reading! ^_^**

**_Chapter Five_**

**_Curtains Up_**

C

A

S

S

Y

Leo and I left the trio on the deck of the big house and headed to the infirmary in the second floor to check on Percy. I was about to open the door when I heard voices talking inside.

"The next great prophecy had begun." I heard my brother said flatly as if he was very tired.

"We should go." Leo whispered to me and was already turning his back to go downstairs, but I grabbed his wrist to stop him.

"Just a moment." I told him.

"You should have told us sooner about meeting a shadowhunter, Percy. Look at what happen to you. What if Cassandra gets hurt as well?" Chiron scolded him.

"I thought if Cassy and I ignore him and their existence maybe we can avoid or at least delay the great prophecy from happening." He responded dejectedly.

"Percy, you know that the great prophecy is inevitable." It was Annabeth who was talking to my brother this time. Her voice was soft and comforting.

"I know that now."

"Cassy." Leo hissed, tugging me away from the door. "Let's go."

"Do you know what they are talking about?" I asked him, still whispering quietly. "What is the great prophecy?"

"I can't tell you. I swear to the river Styx." Leo whispered back, looking very desperate to get away from the on-going conversation on the other side of the door.

"Fine. You can go of if you want to, but I'll stay here to listen" I said stubbornly, letting go of his wrist.

"Cassy."

"Leo," It was not me who called his name but Annabeth, who opened the door of the infirmary. "And Cassy, don't you know better than to listen to other people's conversation?" she scolded us.

"I tried to stop her." Leo defended.

Chiron only sighed at our antic. "Are you sure you are fine, Percy?" He asked my brother.

"Yeah, go ahead and call all the cabins' head counselor for a meeting." Percy answered. He changed into camp shirt as well like me and was sitting on his bed.

"Very well then." Chiron nodded his head and wheeled out of the room leaving the four of us.

"Come here, kiddo." My brother called out, using his nickname for me, patting the space next to him for me to sit down.

I didn't sit down though; instead I ran to him and hugged him tightly. I've seen injured demigods before but not as serious as Percy's, which I have to admit scared the hell out of me. When I let go of him, he had a grin on his face.

I sat down on the bed next to him. "There are a lot of things we need to talk about. First things first, did you also know about the existence shadowhunters? Is that why you wanted me to avoid Jace so much? What's the great prophecy?" I shoot him with my questions right away.

"Chiron told us about them but never meet one until the night we met Jace. I thought avoiding him is the smartest thing to do." He answered.

"The great prophecy tells about the rise of fall of Olympus." Annabeth answered my last question.

"I know about that. What I want to know is what does the great prophecy said." I clarified.

"It's not yet the right time," She responded, meeting my brother's eyes. "And we need to go to the rec room now."

When we arrived at the rec room, Jace, Clary and Isabelle, and almost all of the cabins' head counselors were already there, even Nico that spend most of his time in the Underworld was present, waiting for the meeting to start. Chiron was sitting on the head of the Ping-Pong table, Percy and Annabeth sat down on his left and right side while Leo and I sat down on the vacant chairs next to Jace. After all the head counselors was complete, Chiron started the meeting.

"Before we proceed to discuss about our current problem, I'd like you to meet our new friends Clary Fairchild, Jace and Isabelle Lightwood. They are shadowhunters." Chiron explained to the head counselors that apparently didn't have any idea what was a shadowhunter until today. There were whispers of confusion among the attendees about their participation in the meeting, but Chiron ignored it.

"Now, as you can see Mr. D was called back to Olympus by Zeus because of the current problem in the Underworld." He started to tell us.

"Erebos, the Primordial god of Darkness and Mist, which was turned into the great black wall in the Underworld is set free by the Demon Lords that was imprisoned in hell when they breakthrough the wall of Erebos in the Underworld to escape from hell."

The word darkness bothered me, reminding me of my nightmares, leaving a prickle of cold to my nape down to my spine.

"Wait! What?!" Percy asked, confused by what Chiron said like everyone else. "By hell, you mean Underworld, right?"

"No, hell as in inferno, Percy." Chiron answered.

"Underworld and hell are two different dimensions." Nico spoke up this time. "Where do you think a person that doesn't know about the existence of Underworld go after they die? When a person die their soul goes to the dimension of afterlife they believe in, Underworld and hell are one of the examples of it. I believe that there are many more dimensions out there we have no idea exist."

"It was taught to us about the existence of other dimension but that's just…" Isabelle let her sentence trailed off.

"Mind blowing." Jace supplied.

"You told me once about it when you first take me to the Silent City." Clary reminded him.

He nodded. "What are Demon Lords? I've studies demonology and I never heard or read anything about those kinds of demons before." Jace asked.

"Those Demon Lords were the demons Pandora set free when she opened the jar, because of many demons lurking around our world that time, a warlock named Jonathan Shadowhunter summon the Angel Raziel to create a race of human that can protect the world from the demons. It was also Jonathan Shadowhunter, who imprisoned the Demon Lords in hell with the helped of demigods. After doing it, the two races decided to not interfere with each other's business and erase all records written about one another on their history, including the Demon Lords." Chiron answered.

"So, we have to catch Erebos and throw the Demon Lords back to hell?" Leo asked.

"I wish it's that easy but we must find Sasha, the guardian of the wall first, she is the only one who can fix the wall and imprison Erebos again. My father built only a temporary wall to keep the demons from using it as their escape path." Nico answered this time.

"We'll have to launch a quest to rescue Sasha. It will be our main priority at the moment." Chiron agreed to Nico.

"We need Rachel to tell us the prophecy of the quest but she's in school right now." Annabeth said.

"We can try to call her through Iris message." Percy suggested.

Annabeth fished out a drachma from her pocket while Percy made a rainbow, he tossed the drachma to the rainbow he made and a cloud of mist formed, showing Rachel sitting on her desk in her dorm room.

"Percy," Rachel answered the message cheerfully. "What's with the sudden message?" The tone of her voice change, it was laced with worry now after seeing the grim expressions on our faces.

"We're going to a quest." Percy explained to her about our current situation. "We need you to tell us the –" My brother wasn't able to finished his sentence as Rachel started to pronounce the prophecy of the quest.

"Those who are touch by the angel

Go along the Earth-Shaker and Anvil

To the frozen desert, you must enter the gate of hell

Where the guardian you ought to save waits inside a cell.

One will be left behind alone

To keep the promise that is set in stone"

After Rachel told us the prophecy, the Iris message was cut off. The room was in dead silence for a moment until Jace spoke up.

"In the first couplet, it said those who are touch by the angel, Clary and I both have a mark that symbolized being touch by the angel." Jace said.

"The two of you will do the quest?" Isabelle asked, astonish by their willingness to come along the quest. "I know you two have tendency to make suicidal decisions but this is insane! You can't possible agree to literally go to the depths of hell!" She snapped angrily.

"We're shadowhunters, Isabelle. We face danger everyday this is no different." Jace tried to assured her. "Besides I always want to see hell." A smirk was on his face.

"You're unbelievable!"

"I… I'm going too." I volunteered. I want to sound confident but all I can feel was cold chill down on my spine. I barely noticed everybody's stare at me as I only focus on looking at my brother. I know what they're all thinking, Percy will be a better choice to go with Jace and Clary since he was a veteran at doing quests compare to an amateur like me, but I told myself to held my ground and straighten my spine to look confident even though inside I'm not.

"Poseidon's the Earth-Shaker and I am his daughter." I announced. "I'm also having nightmares with pass few days." I continued to tell them about my dream of disembodied voice in the darkness.

Percy's expression was blank, which was very rare. He was always been an open book. "Are you sure about this?" He asked me seriously.

"Percy! You can't let Cassy go to a dangerous quest like this!" Annabeth protested.

"I am." I answered steadily.

He nodded his head. "If that's what you want."

"Percy!" Annabeth hissed.

"Cassy is a daughter of Poseidon. She had the right to volunteer to join the quest and as the head counselor of Poseidon's cabin I'm giving her my permission." He said authoritatively, which silence Annabeth.

"I'm in too." Leo volunteered too with a goofy grin on his face as if he was actually happy to come along to the rescue mission in hell.

"It's decided then. Jace, Clary, Cassy and Leo will be doing the quest." Chiron announced.

"Antarctica is also known as the frozen desert." Annabeth said, probably analysing the prophecy inside her head now.

"Why would the gate of hell be in frozen place like Antarctica?" Percy asked with a dumb look, shaking his head.

"Hell is cold." I said absentmindedly. Percy and the others stared at me like as if I go mad.

"The ninth circle of hell is cold." Jace said, the corners of his lips turned up to a grin. "It's from Dante's Inferno." He told to everyone.

I looked at him with a small smile. I never thought of Jace as a reader, but the way he knew how I adore books when he brought me to the library came back to me, only those who love books will understand the look on my face that moment. He smiled back, not his usual smug grin but a real sincere smile.

"Can it be true?" Clary asked. "That hell is cold?"

Jace shrugged casually like the thought of going to hell didn't bother him. "How am I supposed to know when I've never been there?" Clary glared at him.

"We're just quoting a passage from a book." I answered Clary's question.

"One of you might be left behind." Isabelle said. "Don't you dare act as the hero, Jace!"

"Nah, I'm no hero, so it's definitely not going to be me."

"And I won't let you, anyway." Clary said.

Percy and I looked at each other silently conversing.

_Percy: I already let you do the quest; don't be stupid to let yourself be left behind. _

_Me: Not gonna promise anything._

_Percy: Cassandra Charmaine McQuee!_

_Me: I'm no hero too; you got nothing to worry about._

_Percy: That makes me worry more; you're the most selfless person I know._

_Me: I am not._

I turned away from my brother's stare and remember my promise to mom not to get involve with the shadow world but look I'm in it more deeply.

Am I doing the right thing?

**A/N: Hi! Thanks for reading! ^_^**

**I'm not sure if they can Iris message a mortal but Percy messaged his mom with it before, so I think that they can do the same for Rachel.**

**Excuse my silly rhyming skill. I'm never been good at rhyming words.**

**I think if I lengthen the chapter it will become too overwhelming so that's it for now!**


End file.
